Dark Matter Phenomenology Across Scales: From Ultralight to WIMPs

This thesis focuses on Dark Matter phenomenology, investigating four particle Dark Matter models, with different physical properties and vastly different phenomenology. The first three chapters introduce the macro-areas of research that are necessary to understand the models: the Standard Model (SM) of particle physics, the standard cosmological model, and the Dark Matter problem. The following chapters focus on the theories studied during the PhD programme. The first two involve axion-like particles (ALPs) with flavour non-universal couplings. In the former, the axion acts as a portal between the SM and the dark sector, mediating a freeze-out. In the latter, the ALP itself is the DM candidate, and is produced via freeze-in. The next project involves the electroweak multiplets of Minimal Dark Matter, studying in detail the phenomenology of this theory and computing prospects for present and future indirect detection searches. The fourth and final project involves the Ultralight Dark Matter candidate and its characteristic soliton, showing how one can obtain new bounds on this candidate using the recent measurement of a stochastic gravitational wave background reported by the NANOGrav collaboration.